Spectral imaging is aimed at providing at least some spectral information about an object at every location in an image plane. Various spectral imaging techniques have been developed, including multispectral imaging, hyperspectral imaging, full spectral imaging, imaging spectroscopy or chemical imaging. Spectral images are often represented as an image cube, a type of data cube.
Multispectral (MS) and hyperspectral (HS) cubes could be acquired in many ways. Some systems (utilizing whiskbroom, pushbroom and tunable filters for realizing HS imagers), rely on multiple acquisitions of 1D or 2D subsets of the 3D HS cube followed by simple reconstruction. Some other systems include polychromatic sensors that trade-off resolution with spectral information (similar to the Bayer CFA) and require spatio-spectral reconstruction algorithms [1], [2].
Recently, several HS snapshot acquisition techniques have been developed. Some of them are based on compressed sensing in which the HS image is assumed to be sparse, and an additional optical element is used within the imaging system, to compress the data [3]-[6]. However, these techniques require prior knowledge of the scene being imaged, and also typically suffer from low light efficiency, and systems implementing such techniques are rather complex.
As for the integral field spectroscopic systems, the common underlying principle of these systems is similar to light field cameras [7] in the sense that the spectral information is traded-off with spatial resolution. Thus, a number of spectral bands in the detected light is equal to the resolution degradation ratio. Integral field hyperspectral imaging techniques, such as lenslet array, fibre array, image slicer and micro-slicer, all exhibit this behavior. Yet another known solution concerns the use of a 2D grating that diverges incident light according to the grating' diffraction order to form multiple, multispectral sub-images on the sensor; this is followed by reconstruction algorithms [8]. This method allows fast hyperspectral cube acquisition, but the resultant image suffers from low spatial resolution; also the required setup could not be integrated in common cameras.